A powershift transmission is a speed and power changing device installed between a power source and a final drive of a work machine. Powershift transmissions are often used in work machines such as, for example, agricultural and industrial machines.
A powershift transmission has lower forward modes and higher forward modes. The lower forward modes are, typically, used for propelling work machines at low speeds. In lower forward modes, an output shaft of the powershift transmission is rotating slowly but with a relatively high amount of torque. On the other hand, the higher forward modes are, generally, for propelling the work machine at high speeds in, for example, transport. In higher forward modes, the output shaft of the powershift transmission is rotating relatively quickly but with a relatively low amount of torque.
It is generally desirable for a powershift transmission to have a high total transmission ratio (i.e., 24:1 or higher) to propel the work machine effectively at both low and high speeds. It is also desirable that the steps, between forward modes, be as small as possible (i.e., 17% or lower). Small steps promote smooth mode changes and enhance operator comfort. It is also desirable for a powershift transmission to have the fewest number of parts possible to minimize production costs.
In the past, powershift transmissions comprising nine clutches and eighteen gears—not including the clutches and gears specifically necessary for reverse modes—usually had either eighteen or twenty forward modes. For example, a first known powershift transmission design had six speed clutches, three range clutches, and eighteen gears for use in forward modes. This first known powershift transmission had only eighteen forward gear modes. As another example, a second known powershift transmission had five speed clutches, four range clutches, and eighteen gears for use in forward motion but had only twenty shiftable gears.